Photometric and Spectroscopic Observations of the Neglected Near-contact Binary Cl* Melotte 111 AV 1224.

This paper presents a photometric and spectroscopic study of the short-period binary star Cl* Melotte 111 AV 1224. Measurements in the B, V, and R passbands obtained during three observing runs between 2014 and 2017 and medium-resolution spectra secured in 2014, are analyzed together with public data from the SuperWASP and LAMOST projects. Our light curves show marked asymmetry with a variable O’Connell effect. The SuperWASP photometry is used to derive a mean binary period of 0.345225 days. The analysis of the (O − C) diagram reveals that the orbital period is decreasing at a rate of dP/dt = −3.87 × 10⁻⁶ days yr⁻¹, which may be caused by mass transfer from the more-massive component to the less-massive one. The system is found to be a single-lined spectroscopic binary with a systemic velocity, γ = 1 ± 3 Km s⁻¹, and a semi-amplitude, K₁ = 21 ± 5 Km s⁻¹. The spectral classification and the effective temperature of the primary component are estimated to be K0V ± 1 and 5200 ± 150 K, respectively. The photometric and spectroscopic solutions reveal that Cl* Melotte 111 AV 1224 is a low-mass ratio (q = m₂/m₁ ∼ 0.11), low-inclination (∼38°), near-contact system. The masses, radii, and luminosity for the primary and secondary are estimated to be 1.02 ± 0.06 M_⊙, 1.23 ± 0.05 R_⊙, 1.01 ± 0.06 L_⊙, and 0.11 ± 0.08 M_⊙, 0.45 ± 0.05 R_⊙, 0.10 ± 0.06 L_⊙, respectively. The marginal contact, together with the period decrease, suggests that this binary system may be at a key evolutionary stage, as predicted by the theory of thermal relaxation oscillations. [ABSTRACT FROM AUTHOR]